As a vehicle for a single person, in the commercial field, a wheelchair is a medical appliance which aids the disabled, patients, the elderly and the infirm to move easily. Wheelchairs are classified into the manual wheelchair which is driven by manpower and the electric chair which uses a motor-drive mechanism.
The wheelchair has driving wheels on both sides of the frame constructing the wheelchair, and has front wheels at the front part or rear wheels at the rear part of the frame so as to move easily.
Meanwhile, generally, the space between the front wheels (or the rear wheel) and the driving wheels of the wheelchair is somewhat narrow, so the wheelchair can change its direction or rotate itself in limited space—in other words the wheelchair is designed to be suitable to move indoors. However, as the space between the wheels which is located along the lengthwise direction is narrow, the movement of the wheelchair is unstable when it moves at a high speed. In addition to the wheelchair stated as an example, since the wheelbase of a movable structure like the form of the wheelchair is fixed, it has some problems wherein the movable structure cannot be used suitably in accordance with its situation.